On such a farm machine that is now known, the tongue comprises at its front part a sort of prismatic cavity determined by three walls, two side walls and a front wall. The upper part of the transmission housing extends inside the prismatic cavity between the three walls and is fastened there by a number of bolts.
In practice, it has been found that this mode of fastening the transmission housing can be liable to loosening of the assembly bolts, in particular the assembly bolts that fasten the transmission housing to the side walls of the prismatic cavity.
This loosening phenomenon is due both to the production tolerances of the upper part of the transmission housing and, especially, to the production tolerances of the prismatic cavity, particularly the tolerances on the inside distance separating the two side walls.
Since the tongue is a mechanically welded part, the production tolerances must be relatively broad. Thus, during tightening of the side assembly bolts, the side walls are first deformed a certain amount before they come in contact with the upper part of the transmission housing. It is then found that an elastic assembly instead of a solid assembly is obtained, due to the elastic deformation of the side walls.
In addition, the assembly bolts which fasten the transmission housing to the side walls are subject to shear stress.
It is then understood, considering the facts:
(1) that the entire tractive force needed to draw the machine goes through the assembly bolts;
(2) that the resulting assembly is generally an elastic assembly; and
(3) that the side bolts are subjected to shear stress, that the vibrations produced by the configuration of the ground on which the machine travels during work causes loosening of the side bolts--which, of course, is not desirable.
Moreover, the known assembly mode does not allow a fast and easy mounting. This is because, during the entire operation of introducing and tightening the bolts, it is necessary to hold the transmission housing by positioning it exactly so that the bolts can be introduced into the corresponding threaded holes. Therefore, it will be understood, considering the relatively heavy weight of the transmission housing, that its mounting is long and expensive.